Polyhexamethylene Guanidine (PHMG) is a high-molecular-weight cationic polymer with the chemical formula (C7H15N3)n·x(HCl) and CAS No. 57028-96-3. Its positively charged guanidine groups achieve broad-spectrum antimicrobial activity by adsorbing onto negatively charged microbial cell membranes, thereby disrupting cell wall permeability and metabolic enzyme activity. It exhibits a Minimum Inhibitory Concentration (MIC) as low as 0.5–2 ppm against Gram-positive bacteria and molds, and possesses a decomposition temperature exceeding 222°C, making it suitable for applications requiring long-term antimicrobial protection.
Analysis of Core Characteristics:
1. Antimicrobial Efficacy and Safety: It achieves rapid microbial elimination by dissolving cell membrane lipids and blocking ATP synthesis; it demonstrates a kill rate of >99.9% against *Staphylococcus aureus* and *Escherichia coli*. With an acute oral LD50 of >5000 mg/kg and no sensitization reactions observed in skin irritation tests, it meets the low-toxicity requirements for building materials.
2. Physicochemical Stability: Its aqueous solution maintains a pH of 6.5–8.5 and a viscosity of 5 mPa·s at 25°C. It is compatible with non-ionic surfactants and remains functionally stable within a temperature range of 20–100°C, making it suitable for mold prevention in heat-sensitive building materials.
3. Environmental Friendliness: It boasts a biodegradation rate of >90% and generates zero VOC emissions. It has received approval under the EU Biocidal Products Regulation (BPR) and for food-contact materials by the U.S. FDA. Unlike quaternary ammonium salts, it poses no risk of inducing microbial resistance, making it suitable for long-term, repetitive use.
Application Scenarios in the Building Materials Sector:
1. Enhanced Wood Mold Prevention: The addition of a 0.5% solution extends the mold-free lifespan of plywood and medium-density fiberboard (MDF) to 12 months. Experimental data from one manufacturer demonstrated that the mold incidence rate in Chinese fir samples was reduced from 78% to 3.2%.
2. Functional Upgrades for Structural Adhesives: At an addition rate of 0.3%–0.8%, it extends the curing time of neutral silicone sealants by no more than 15%. Furthermore, it maintains a shear strength retention rate of >92% for aluminum-to-glass bonds, with the area of adhesive bond failure increasing by only 3.7% after exposure to humid-heat aging conditions.
3. Antimicrobial Upgrades for Coatings: When blended with water-based acrylic emulsions to produce antimicrobial coatings, it generates an inhibition zone diameter of 21 mm against *Aspergillus niger*, thereby meeting the requirements of the GB/T 21866 standard. 4. Stone Penetration Protection: Following the incorporation of a nanosilica carrier, the contact angle of marble increased from 62° to 108°, and the killing rate against *Bacillus subtilis* exceeded 90%.
A comparison of technical parameters demonstrates that PHMG outperforms benzalkonium chloride and hydrogen peroxide in terms of MIC, thermal stability, compatibility with building materials, duration of sustained antibacterial activity, and migration levels within adhesives.
